Rotating joint assembly



Oct. 25, 1966 A. DORNE ROTATING JOINT ASSEMBLY Filed May 26, 1964 2 Sheets-Sheet 2 3/64 I632 CENTER l CONDUCTOR l 1 I ANTENNA I v ANTENNA GABLE\ I CABLE I I u I loe i J I k 6/ TRANSFORMER 6/ I GAP ANTENNA ;/56 CAVITY L E t REGEIVER CAVITY I y /5 RECEIVER CABLE FIG. 2

United States Patent 3,281,728 ROTATING .lOINT ASSEMBLY Arthur Dome, Sea Cliff, N.Y., assiguor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed May 26, 1964, Ser. No. 370,384 5 Claims. (Cl. 333-98) This invention relates to rotating radio frequency joints and, more particularly, to a non-coupling rotating joint that permits the transmission of radio frequency energy simultaneously between an assembly of two or more independent rotating antennas.

In microwave systems it is usually necessary to provide efficient coupling between the radio frequency transmission line and the transmitting or receiving antennas. The mounting of the difierent elements of the microwave components and the searching and scanning motions of the antennas require joints, between the feeding radio frequency transmission lines and the antenna, to have various degrees of freedom. Couplings of this sort are required to provide a good impedance match for all required joint displacements and to minimize the radio frequency leakage from the joint in order that the maximum transfer of energy from waveguide to antenna occurs. In radar applications, especially of the airborne type, it is necessary to have a unit of a compact size and weight. Further, in some types of radar application it is desirable to have a plurality of antennas in a vertical array and to have these antennas capable of rotational movement about their vertical axes.

Prior art rotating joints are not applicable whenever it is desirable to have the antennas rotate at high speeds. In some types of prior art rotating joints, the speed of rotation remains fairly low because of the necessity of using berrylium, copper or Phosphor bronze springs which are slotted to form contact fingers. These fingers, under tension, provide a good electrical and mechanical wiping contact. Another disadvantage of this sort of design is the limited amount of power at which these joints are operable. At high power, arcing and sparking may take place at the contact areas, thus destroying the electrical conductivity of the surface.

Other prior art rotary joints have been developed which have no sliding contacts. One type uses a configuration in which a coaxial line crosses the waveguide. Joints of this type have the disadvantage of being frequency sensitive and, therefore, they have very limited application.

Another prior art device is the use of probe transition from coaxial line to waveguide. Construction of joints of this sort yield a fairly good impedance match and a fairly wide frequency bandwidth. The disadvantage occurring in this arrangement is the necessity of accurately holding the probe depth and centering the probe to the predesigned value.

The instant invention overcomes the forementioned disadvantages of the prior art by providing a simple and eflicient apparatus for coupling a waveguide or coaxial feed line to a rotating antenna or a plurality of rotating antennas.

The joint is adaptable to have a plurality of joints by vertically stacking one joint on another. The joints have both stator and rotor elements. The stator element carries a plurality of coaxial RF feed lines to a number of receiver cavities and a single RF feed line is connected to excite each receiver cavity. The rotor element is mounted on bearings that allow free rotation about the stator element and is mounted so that it partially encloses and is adjacent the receiver cavity. The two cavity elements are electrically coupled by a waveguide transformer 3,281,723 Patented Oct. 25, 1966 configuration. The joint has no sliding electrical contact surfaces between the stator and rotor and allows any number of channels to be fed through the stator and coupled to a single or a plurality of antennas for each channel.

An object of the present invention is the provision of an RF feed line to a rotating antenna that is of simple and compact design.

Another object of the present invention is the provision of a rotary joint that is capable of feeding an RF feed line to a plurality of rotating antennas.

Still another object of the present invention is the provision of a rotary joint that couples a scanning antenna to a stationary RF feed source without the need of sliding electrical contact surfaces.

A further object of the present invention is the provision of a rotary joint that is easily adaptable to vertical stacking in order that a larger number of channels may be incorporated into a single unit.

Another object of this invention is to couple efiiciently a plurality of stationary coaxial lines to a plurality of rotating antennas.

Another object of this invention is to provide a technique of transmission of high frequency energy simultaneously between an assembly of two or more independent rotating antennas.

A further object of this invention is to provide a coupling that permits a proper impedance match to both coupled members for all relative rotational positions therebetween.

Another object of the present invention is to provide a stacked antenna array that rotates about its vertical axis and that has no radio frequency energy leakage through the bearing.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a cross section of a preferred embodiment of the invention;

FIG. 2 is a functional diagram of the rotary joint.

Referring to FIG. 1, it can be seen that the non-contacting, rotating radio frequency joint is made up of two general sections; one stationary, referred to hereinafter as the stator element and the other rotating, hereinafter referred to as the rotor. The non-rotating section is positioned to form a central support for the rotating section. The stator 11 is a tubular member which may be fastened or attached to an external fixed support by means of the lower threaded portion or fastened to a fixed support by other techniques known to those skilled in the art. Secured to the end of this tubular member and enclosing the said end is a circular end plug 12 fastened to the inner wall of the stator by any appropriate means known to those skilled in the art. Four end connector cable adapters extend through and are insulated from the plug section by conventional means. Only two of the cable adapters are shown in the drawing, adapters 13 and 14, respectively. The stator 11 extends upwardly from the threaded portion to form a circular outer support frame work 18. Also extending from the tubular stator member 11 is a wall 17 which forms the chamber wall for the A-band receiver cavity 101. Extending over this wall and fastened rigidly to the wall, by means known to those skilled in the art, is a generally tubular insulating sleeve 19. This sleeve 19 may be held to the receiver cavity 17 by means of a force fit, if desired. The outer support frame work 18 forms a boxlike chamber but does not contact the insulating sleeve at its upper portion. Member 18 provides a protecting cover for the end of insulating sleeve element 19. In addition, since it is the same size as receiver cavity it also will protect the receiver cavity wall 17. The receiver cavity 101 is formed so that it has a tubular extension extending from its top portion down into substantially the center of the cavity. At the bottom of the receiver cavity 101 is an aperture 61 which allows coaxial cab-ling to travel through the center portion of the stator. Coaxial cables 15 for conducting RP energy are fastened to the end connector adapters and extend through the aperture 61 in the base of the receiver cavity and upward through the center of the stator section 11. This cavity will be referred to hereinafter as the A-band receiver cavity. The appropriate coaxial cable for the A-band energy is electrically fastened to the tubular extension 106 at 56. A short section of waveguide 109 and 110, respectively is formed by the top wall portion of the receiver cavity and the lower portion of circular structural support spacers 42.

The next cavity section, hereinafter designated as the B-band cavity 103, is fabricated so that it is centrally located in the interior of the insulating sleeve 19. Numerous spacers 43 and 45 rigidly hold the B-band cavity in position. The receiver cavity wall 44 of the B-band cavity is press fitted in a necked down portion 62 of the insulating sleeve. The B-band cavity has essentially the same shape and structure as the A-band cavity. The cabling 15 from the end connectors 13 and 14, respectively, extend through apertures in the spacing members 42, 43 and the bottom of the B-band cavity. The appropriate coaxial line for transmission of B-band energy is electrically fastened at 57 to the tubular extension 107 in the same way as the A-band coaxial cable.

A short section of waveguide 111 and 112, respectively is formed in much the same way as in the A-band receiver cavity 101 by the top wall of the receiver cavity wall 44 and the lower wall of structural support member 46.

Positioned above the B-band cavity 103 is the C-band cavity 105, which has the cavity Wall 52 rigidly attached in the necked down portion 63 of the insulating sleeve 19. Suitable support members, not numbered, rigidly attach and hold the C-band cavity in a centrally located position with respect to the insulating sleeve 19. A section of the cavity wall 52 is secured at its lower section to the insulating sleeve by fastening means such as pointed out above. The cabling 15 is extended in much the same manner as in the A-band cavity, through apertures provided in the support means and in the cavity bottom of C-band cavity 105. The appropriate coaxial cable for the C-band energy is electrically fastened to the cavity wall at 58. The top portion of the waveguide wall 52 and the lower wall of one of cylindrical support members 55 forms a short section of waveguide 113 and 114, respectively. Numerous other cylindrical support members 55 extend upward to the top of the insulating member 10. These supports 55 serve to hold the D-band cable in a centrally located position with respect to the insulating sleeve 19. The coaxial cable is electrically connected to element 53 for directing or receiving D-band energy from the horn assembly 28.

The rotating section of ground plane 16 and cone 23 are supported by bearing 26. The outer race of bearing 26 is fixed to cone 23 by cone cap 25. These elements are joined by any appropriate fastening means known to those skilled in the art but are shown in the figure as fastened by riveting. The inner race 27 is rigidly attached to a bushing 29 which is rigidly attached by any appropriate means to the central necked down portion of the insulating sleeve 19. This construction allows 360 rotation of the cone 23 and the ground plane 16 about the stator member 11. A cone cap 25 is fabricated to be rigidly fastened to cone support 24 and has a section at its upper end formed for two waveguides connection outputs 30. Above these waveguide connections is a cylindrical section 51 over which the horn 28 is fitted and attached. The section 51 is spaced a predetermined distance from insulation member 19. This construction allows the horn 28 to be rigidly attached to the cone cap and allows rotation of the horn assembly 28 with the cone 23. The lower part of the rotor section is held to the outer race of bearing 26 by means of cone support 24-. The cone support members are fabricated to extend downwardly to the ground plane where they are attached to a cone flange 21 by a cone ring 22. These elements are shown as fastened by rivets but other types of fastening may be used.

Fastened to the lower portion of cone support 24 is a metal structural frame work 31 which extends downwardly and adjacent the insulating sleeve 19. This frame work forms the outer wall assembly of the rotating part of the B-band cavity; hereinafter designated as antenna cavity 104. Attached to the outer wall 31, by appropriate means, are coaxial connectors 32. Also attached to wall section 31 is an inner wall section 33-. These walls together form B-band antenna cavities 104 and 115, respectively. These two cavities are structurally formed so as to provide a neat structure which fits adjacent the insulating sleeve portion.

The A-band portion of the rotating part of the coupling joint is formed as a cylindrical member 34; adjacent and encircling sleeve 19. This cylindrical member 34- is separated by a space 64 which isolates it from the lower portion 62 of the B-band cavity assembly. Attached to the lower portion of the cylindrical member 34 is another cylindrical assembly 36 which forms the cavity wall of the rotating part of A-band assembly. On the upper portion of the cavity wall 36 is fastened two coam'al output terminals 35 and 40, respectively. These terminals are held in place by rivets to the cavity wall 36. A center terminal 39 from the coaxial connector 35 extends into A-band antenna cavity 102 and in like manner a center terminal 41 extends from coaxial connector 40 to A-band antenna cavity 100. The two chambers which are formed by wall member 36 are held in a position adjacent the insulating member by structural members 37 and 38. These two members are fastened by rivets or other means to the structural cone member 23. An opening in the cavity wall of the rotating A-band cavities and 102 are adjacent the waveguide sections 103 and 110, respectively which are formed in the stator member by structural member 42 and the top of wall 17 of the receiver cavity 101 to provide a means for transferring energy to or from the cavity. This sort of fabrication allows the A-band cavity member and its cylindrical member to rotate freely with the cone structural members about the stator member.

The ground plane member 16 is provided with internal threads on its lower portion. A bushing, not shown, may be threaded in this section. The internal cylindrical portion of the bushing would have a bearing surface to mate with the other surface of the stator 11 in order that the least possible friction exists between it and the outer surface of the cylindrical portion of the stator 11. This allows substantially frictionless rotation of the cone portion about the stator member 11 without having any side play or binding existing at the lower portion of the ground plane and the stator member.

Operating principles of the rotating joint may best be understood by referring to FIG. 2. This figure shows the basic structure of a typical joint unit of the rotating joint assembly as shown in FIG. 1. Examination of this figure will show that there are two coaxial type cavities in each joint. One of the cavities is comparatively long and thin and is partially enclosed by the other; this cavity hereinafter referred to as the receiver cavity. The receiver cavity, of course, being the non-rotating or stator member. The other cavity which is relatively broad and short and which rotates about the stator member is hereinafter referred to as the antenna cavity. The receiver cavity is excited by the coaxial cable from the receiver sytem, not shown. The rotating outer chambers or the antenna cavities are excited by two coaxial cables coming from antennas 163 and 164, respectively. These coaxial cables are attached to the respective antenna cavities at 39 and 41. The two cavities, receiver and antenna, are electrically connected by a transformer which consists of a section of coaxial transmission line and a short section of parallel plate radial line in series.

Referring now to FIG. 2, it can be seen that the transmission line portion of this transformer lies inside the upper portion of the center member 106 of the receiver cavity 101. The center conductor of this inner transmission line passes through the top surface of the antenna cavity 100, 102 at one end. The center conductor then extends out beyond the inner transmission line outer conductor 106 at the other end to form the lower portion of the center conductor of the receiver cavity 101, and finally passes through the wall 17 at the bottom surface of the receiver cavity. Between the antenna cavity 100, 102 and the transformer is a narrow gap 61 which separates the stator and rotor. Assuming the gap 61 to be of negligibly low impedance, the circuit is equivalent to a length of transformer shunted at each end by a cavity extending between the two parallel antenna cables at one end and the receiver cable at the other. The gaps are a half wave length long at the operating frequency of the joint and has at their center a high impedance cavity inserted in series relationship. Rotary joints using half wave length gaps are well known in the art and described in the literature, for example, volume IX of the Radiation Laboratory Series, Microwave Transmission Circuits, McGraw-Hill, 1948.

The two lower sections of the rotating joint assembly of FIG. 1 are both of the above types. The two upper joints are constructed slightly different. Each of these are connected to its corresponding antenna, now shown, by means of a microwave guide rather than coaxial lines. In these cases, the antenna cavity is replaced by a short circuited section of waveguide. Furthermore, in the case of the top units, because no cable need be fed through, the unit has been simplified. The top of the center cable connected to element 53 need not have any waveguide and also does not need any gaps. Thus, the above structure makes feasible a large number of changes in a single unit and thereby provides operation over a very broad band of operating frequencies.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A non-contacting rotating radio frequency joint assembly comprising:

a first stationary chamber having a relatively long thin shape and formed with an aperture in one of the chamber Walls;

radio frequency energy transmission means electrically coupled to an interior wall of said chamber for pro viding excitation of said chamber;

second chamber means having a relatively short broad shape and formed with an aperture in one of its walls;

said second chamber partially enclosing said first stationary chamber and adapted to rotate about said first stationary chamber;

gap means electrically coupled on either side of said rotating chamber and in series with said rotating chamber for providing high impedance to radio frequency energy;

said gap means each having a physical dimension of a half wave length to the operating radio frequency of the rotating chamber; and

transformer means electrically coupling said rotating chamber to said stationary chamber at each of said respective chambers apertures;

whereby energy received by the rotating chamber is transmitted via the transformer means to the stationary chamber.

2. A non-contacting rotating radio frequency joint assembly as claimed in claim 1 wherein the first stationary chamber is a microwave cavity.

3. A non-contacting rotating radio frequency joint assembly as claimed in claim 1 wherein the second chamber is a microwave cavity.

4. A multiple channel rotary joint assembly comprising a plurality of individual single channel rotary joints as claimed in claim 1 wherein each one of said joints are stacked in axial alignment and wherein the individual joints are fed by radio frequency energy tranmission means which pass through the center of each stationary chamber.

5. A multiple channel rotary joint assembly comprising a plurality of individual single channel rotary joints as claimed in claim 1 wherein the second chamber is a microwave cavity capable of rotating and which is excited by radio frequency energy from individual antennas positioned on the ground plane of the assembly.

References Cited by the Examiner Fromm, W. E., A New Microwave Rotary Joint, IRE National Convention Record, vol. 6, part 1, pages 78-82.

HERMAN KARL SAALBACH, Primary Examiner. L. ALLAHUT, Assistant Examiner. 

1. A NON-CONTACTING ROTATING RADIO FREQUENCY JOINT ASSEMBLY COMPRISING: A FIRST STATIONARY CHAMBER HAVING A RELATIVELY LONG THIN SHAPE AND FORMED WITH AN APERTURE IN ONE OF THE CHAMBER WALLS; RADIO FREQUENCY ENERGY TRANSMISSION MEANS ELECTRICALLY COUPLED TO AN INTERIOR WALL OF SAID CHAMBER FOR PROVIDING EXCITATION OF SAID CHAMBER; SECOND CHAMBER MEANS HAVING A RELATIVELY SHORT BROAD SHAPE AND FORMED WITH AN APERTURE IN ONE OF ITS WALLS; SAID SECOND CHAMBER PARTIALLY ENCLOSING SAID FIRST STATIONARY CHAMBER AND ADAPTED TO ROTATE ABOUT SAID FIRST STATIONARY CHAMBER; GAP MEANS ELECTRICALLY COUPLED ON EITHER SIDE OF SAID ROTATING CHAMBER AND IN SERIES WITH SAID ROTATING CHAMBER FOR PROVIDING HIGH IMPEDANCE TO RADIO FREQUENCY ENERGY; SAID GAP MEANS EACH HAVING A PHYSICAL DIMENSION OF A HALF WAVE LENGTH TO THE OPERATING RADIO FREQUENCY OF THE ROTATING CHAMBER; AND TRANSFORMER MEANS ELECTRICALLY COUPLING SAID ROTATING CHAMBER TO SAID STATIONARY CHAMBER AT EACH OF SAID RESPECTIVE CHAMBER''S APERTURES; WHEREBY ENERGY RECEIVED BY THE ROTATING CHAMBER IS TRANSMITTED VIA THE TRANSFORMER MEANS TO THE STATIONARY CHAMBER. 